Channel condition estimation

ABSTRACT

There is provided mechanisms for obtaining channel conditions per antenna element, A method is performed by a wireless radio transceiver device comprising N antenna elements in an antenna array with analog beamforming and being configured to communicate using beams. The method comprises obtaining, for a stationary radio propagation channel, channel conditions for signals received by the wireless radio transceiver device in M beams, where M&gt;1. The method comprises transforming the channel conditions for the M beams to channel conditions for the N antenna elements by using a relation based on beamforming weights that map the N antenna elements to the M beams.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application is a 35 U.S.C. § 371 National Stage of InternationalPatent Application No. PCT/EP2016/082720, filed Dec. 27, 2016,designating the United States, the disclosure of which is incorporatedby reference.

TECHNICAL FIELD

Embodiments presented herein relate to a method, a radio transceiverdevice, a computer program, and a computer program product for obtainingchannel conditions per antenna element of the radio transceiver device.

BACKGROUND

In communications networks, there may be a challenge to obtain goodperformance and capacity for a given communications protocol, itsparameters and the physical environment in which the communicationsnetwork is deployed.

For example, for future generations of mobile communications systemsfrequency bands at many different carrier frequencies could be needed.For example, low such frequency bands could be needed to achievesufficient network coverage for wireless radio transceiver devices andhigher frequency bands (e.g. at millimeter wavelengths (mmW), i.e. nearand above 30 GHz) could be needed to reach required network capacity. Ingeneral terms, at high frequencies the propagation properties of theradio channel are more challenging and beamforming both at the accessnode of the network and at the wireless radio transceiver devices mightbe required to reach a sufficient link budget.

The wireless radio transceiver devices could implement beamforming bymeans of analog beamforming, digital beamforming, or hybrid beamforming.Each implementation has its advantages and disadvantages. A digitalbeamforming implementation is the most flexible implementation of thethree but also the costliest due to the large number of required radiochains and baseband chains. An analog beamforming implementation is theleast flexible but cheaper to manufacture due to a reduced number ofradio chains and baseband chains compared to the digital beamformingimplementation. A hybrid beamforming implementation is a compromisebetween the analog and the digital beamforming implementations. As theskilled person understands, depending on cost and performancerequirements of different wireless radio transceiver devices, differentimplementations will be needed.

Different antenna architectures for different frequency bands are beingdiscussed for wireless radio transceiver devices. At high frequencybands (e.g. above 15 GHz) something called “panels” are being discussed.These panels may be uniform linear/rectangular arrays (ULAs/URAs), forexample steered by using analog phase shifters. In order to get coveragefrom different directions, multiple panels can be mounted on differentsides of the wireless radio transceiver devices.

Even though wireless radio transceiver devices may be stationary, andexperience a fairly stationary radio propagation channel it might bechallenging for a wireless radio transceiver device applying analog orhybrid beamforming to find the optimal (or close to optimal) phasesettings per antenna element in order to maximize some metrics (forexample user throughput) due to lack of sufficient channel stateinformation and too many possible phase settings.

Hence, there is still a need for improved channel condition estimation.

SUMMARY

An object of embodiments herein is to provide channel conditionestimation per antenna element.

According to a first aspect there is presented a method for obtainingchannel conditions per antenna element. The method is performed by awireless radio transceiver device comprising N antenna elements in anantenna array with analog beamforming and being configured tocommunicate using beams. The method comprises obtaining, for astationary radio propagation channel, channel conditions for signalsreceived by the wireless radio transceiver device in M beams, where M>1.The method comprises transforming the channel conditions for the M beamsto channel conditions for the N antenna elements by using a relationbased on beamforming weights that map the N antenna elements to the Mbeams.

Advantageously this provides efficient estimation of channel conditionsper antenna element even though only channel conditions for the beamsare available.

Advantageously this enables estimation of channel conditions in theantenna element space despite the use of analog or hybrid beamforming.

Advantageously this enhances the performance for a wireless radiotransceiver device using analog or hybrid beamforming in case ofstationary radio propagation channels.

According to a second aspect there is presented a radio transceiverdevice for obtaining channel conditions per antenna element. The radiotransceiver device comprises N antenna elements in an antenna array withanalog beamforming and is configured to communicate using beams. Theradio transceiver device further comprises processing circuitry. Theprocessing circuitry is configured to cause the radio transceiver deviceto obtain, for a stationary radio propagation channel, channelconditions for signals received by the wireless radio transceiver devicein M beams, where M>1. The processing circuitry is configured to causethe radio transceiver device to transform the channel conditions for theM beams to channel conditions for the N antenna elements by using arelation based on beamforming weights that map the N antenna elements tothe M beams.

According to a third aspect there is presented radio transceiver devicefor obtaining channel conditions per antenna element. The radiotransceiver device comprises N antenna elements in an antenna array withanalog beamforming and is configured to communicate using beams. Theradio transceiver device further comprises processing circuitry and astorage medium. The storage medium stores instructions that, whenexecuted by the processing circuitry, cause the radio transceiver deviceto perform operations, or steps. The operations, or steps, cause theradio transceiver device to obtain, for a stationary radio propagationchannel, channel conditions for signals received by the wireless radiotransceiver device in M beams, where M>1. The operations, or steps,cause the radio transceiver device to transform the channel conditionsfor the M beams to channel conditions for the N antenna elements byusing a relation based on beamforming weights that map the N antennaelements to the M beams.

According to a fourth aspect there is presented a radio transceiverdevice for obtaining channel conditions per antenna element. The radiotransceiver device comprises N antenna elements in an antenna array withanalog beamforming and is configured to communicate using beams. Theradio transceiver device further comprises an obtain module configuredto obtain, for a stationary radio propagation channel, channelconditions for signals received by the wireless radio transceiver devicein M beams, where M>1. The radio transceiver device further comprises atransform module transform the channel conditions for the M beams tochannel conditions for the N antenna elements by using a relation basedon beamforming weights that map the N antenna elements to the M beams.

According to a fifth aspect there is presented a computer program forobtaining channel conditions per antenna element, the computer programcomprising computer program code which, when run on a radio transceiverdevice comprising N antenna elements in an antenna array with analogbeamforming and being configured to communicate using beams, causes theradio transceiver device to perform a method according to the firstaspect.

According to a sixth aspect there is presented a computer programproduct comprising a computer program according to the fifth aspect anda computer readable storage medium on which the computer program isstored. The computer readable storage medium could be a non-transitorycomputer readable storage medium.

It is to be noted that any feature of the first, second, third, fourth,fifth and sixth aspects may be applied to any other aspect, whereverappropriate. Likewise, any advantage of the first aspect may equallyapply to the second, third, fourth, fifth and/or sixth aspect,respectively, and vice versa. Other objectives, features and advantagesof the enclosed embodiments will be apparent from the following detaileddisclosure, from the attached dependent claims as well as from thedrawings.

Generally, all terms used in the claims are to be interpreted accordingto their ordinary meaning in the technical field, unless explicitlydefined otherwise herein. All references to “a/an/the element,apparatus, component, means, step, etc.” are to be interpreted openly asreferring to at least one instance of the element, apparatus, component,means, step, etc., unless explicitly stated otherwise. The steps of anymethod disclosed herein do not have to be performed in the exact orderdisclosed, unless explicitly stated.

BRIEF DESCRIPTION OF THE DRAWINGS

The inventive concept is now described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram illustrating a communications networkaccording to embodiments;

FIG. 2 schematically illustrates a wireless radio transceiver deviceaccording to an embodiment;

FIGS. 3, 4, and 5 are flowcharts of methods according to embodiments;

FIG. 6 is a schematic diagram showing functional units of a wirelessradio transceiver device according to an embodiment;

FIG. 7 is a schematic diagram showing functional modules of a wirelessradio transceiver device according to an embodiment;

FIG. 8 schematically illustrates an access node according to anembodiment;

FIG. 9 schematically illustrates a wireless device according to anembodiment; and

FIG. 10 shows one example of a computer program product comprisingcomputer readable storage medium according to an embodiment.

DETAILED DESCRIPTION

The inventive concept will now be described more fully hereinafter withreference to the accompanying drawings, in which certain embodiments ofthe inventive concept are shown. This inventive concept may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein; rather, these embodiments areprovided by way of example so that this disclosure will be thorough andcomplete, and will fully convey the scope of the inventive concept tothose skilled in the art. Like numbers refer to like elements throughoutthe description. Any step or feature illustrated by dashed lines shouldbe regarded as optional.

FIG. 1 is a schematic diagram illustrating a communications network 100comprising an access node 300 a providing network access to a wirelessradio transceiver device 200, and, optionally, at least one furtheraccess node 300 b. The wireless radio transceiver device 200 is assumedto comprise at least one receiver chain and is configured to receivesignals from the access node 300 a in M beams 110 a, 110 b, . . . ,110M. The wireless radio transceiver device 200 is thus configured tocommunicate in M beams 110 a, 110 b, . . . , 110M (in contrast toomnidirectional beams).

The access node 300 a, 300 b could be any of a radio access networknode, radio base station, base transceiver station, node B, evolved nodeB, g node B, or access point. The wireless radio transceiver device 200could be any of a wireless device, mobile station, mobile phone,handset, wireless local loop phone, user equipment (UE), smartphone,laptop computer, tablet computer, wireless sensor, or another radioaccess network node e.g. for providing wireless backhaul.

FIG. 2 illustrates the wireless radio transceiver device 200 accordingto an embodiment. The wireless radio transceiver device 200 is equippedat least one receiver chain 130, each comprising its own basebandprocessing (BPP) chain 140. Each baseband processing chain 140 isoperatively connected to its own analog beamformer 150. Each analogbeamformer 150 has its own set of analog precoder weights (e.g. definedby a codebook) by means of which the M different directional beams 110a, 110 b, . . . , 110M can be formed. Hence, in the illustrative exampleof FIG. 2, the analog beamformer 150 switches between M analogprecoders; AP1 for generating beam 110 a, AP2 for generating beam 110 b,and APM for generating beam 110M.

The radio transceiver device 200 further comprises N antenna elements,two of which are identified at reference numerals 160 a, 160N. The phaseand gain for each of the N antenna elements 160 a, 160N could beindividually controlled by a phase and/or gain control function. Forexample, according to the illustrative example of FIG. 2, each of the Nantenna elements 160 a, 160N could have its own phase shifter andamplitude taper, although it could be enough to just have phase shiftersfor N−1 of the N antenna elements. The antenna elements 160 a, 160N atthe wireless radio transceiver device 200 might be implemented in anirregular fashion and the physical structure of the wireless radiotransceiver device 200 might affect the radiation patterns of theantenna elements 160 a, 160N.

The embodiments disclosed herein relate to mechanisms for obtainingchannel conditions per antenna element of the wireless radio transceiverdevice 200. In order to obtain such mechanisms there is provided a radiotransceiver device 200, a method performed by the radio transceiverdevice 200, a computer program product comprising code, for example inthe form of a computer program, that when run on a radio transceiverdevice 200, causes the radio transceiver device 200 to perform themethod.

FIGS. 3 and 4 are flow charts illustrating embodiments of methods forobtaining channel conditions per antenna element of the wireless radiotransceiver device 200. The methods are performed by the radiotransceiver device 200. The methods are advantageously provided ascomputer programs 1020.

Reference is now made to FIG. 3 illustrating a method for obtainingchannel conditions per antenna element of the wireless radio transceiverdevice 200 as performed by the radio transceiver device 200 according toan embodiment.

The wireless radio transceiver device 200 comprises N antenna elements160 a, 160N in an antenna array with analog beamforming 150 and isconfigured to communicate using beams 110 a, 110 b, 110M.

The use of analog beamforming 150 allows channel conditions for signalsreceived by the wireless radio transceiver device 200 in M beams 110 a,110 b, 110M to be obtained by the wireless radio transceiver device 200.Hence, the wireless radio transceiver device 200 is configured toperform step S104:

S104: The wireless radio transceiver device 200 obtains, for astationary radio propagation channel, channel conditions for signalsreceived by the wireless radio transceiver device 200 in M beams 110 a,110 b, 110M, where M>1. Examples of how the channel conditions for thesignals can be obtained will be disclosed below.

The M beams 110 a, 110 b, 110M could be non-overlapping or partlyoverlapping, and generally be directed towards the access node 300 a, orat least in directions from which signals from the access node 300 a arereceived by the wireless radio transceiver device 200, or in directionssuch as to obtain as complete channel conditions of the radiopropagation channel as possible.

However, channel conditions for the N antenna elements 160 a, 160N canbe determined despite the use of analog (or hybrid) beamforming bytransforming the channel conditions for the M beams into channelconditions for the N antenna elements. Hence, the wireless radiotransceiver device 200 is configured to perform step S106:

S106: The wireless radio transceiver device 200 transforms the channelconditions for the M beams 110 a, 110 b, 110M to channel conditions forthe N antenna elements 160 a, 160N by using a relation. The relation isbased on beamforming weights that map the N antenna elements 160 a, 160Nto the M beams 110 a, 110 b, 110M. Examples of how the relation used instep S106 can be realized will be disclosed below.

Embodiments relating to further details of obtaining channel conditionsper antenna element of the wireless radio transceiver device 200 asperformed by the radio transceiver device 200 will now be disclosed.

With reference to FIG. 2, the beamforming weights could be regarded asbeing precoder weights; the terms beamforming weights and precoderweights could thus be used interchangeably.

In some aspects the radio propagation channel is sufficiently static(such as being free from fast fading) when the channel conditions forthe M beams 110 a, 110 b, 110M are obtained. This requires the channelcoherence time to be larger or equal to the observation (measurement)time.

Reference is now made to FIG. 4 illustrating methods for obtainingchannel conditions per antenna element of the wireless radio transceiverdevice 200 as performed by the radio transceiver device 200 according tofurther embodiments. It is assumed that steps S104, S106 are performedas described above with reference to FIG. 3 and a thus repeateddescription thereof is therefore omitted.

The radio transceiver device 200 could need to verify that the radiopropagation channel to the access node 300 a is stationary enough. Thiscould for example be achieved by the radio transceiver device 200performing measurements on the radio propagation channel for somedifferent time samples and evaluating how much the radio propagationchannel has changed over time. Hence, according to an embodiment thewireless radio transceiver device 200 is configured to perform stepS102:

S102: The wireless radio transceiver device 200 verifies that the radiopropagation channel is stationary when obtaining the channel conditionsfor the M beams 110 a, 110 b, 110M.

This could for example be supported by using sensors in the radiotransceiver device 200 that evaluate if the radio transceiver device 200is physically stationary.

According to an embodiment, if the radio propagation channel has changedless than some specified value (compared to a certain threshold) theradio propagation channel the radio propagation channel assumed to bestationary enough. In another embodiment the radio transceiver device200 measures and evaluates if the radio propagation channel isstationary enough, for example more stationary than a given threshold.

The radio transceiver device 200 starts sweeping M beams 110 a, 110 b, .. . , 110M (for example beams based on the Discrete Fourier Transform(so-called DFT beams)) and estimates the radio propagation channel forthese M beams. The M beams could be created by the radio transceiverdevice 200 applying phase-only precoders by appropriate settings of theanalog phase shifters.

The radio transceiver device 200 may need to sweep M≥N beams in order toattain individual channel estimates for an array with N antennaelements.

When the measurements are done the radio transceiver device 200 can usebelow Equation (1) and Equation (2) to transform the channel estimatesfor the M beams to N channel estimates (i.e., one channel estimate foreach of the N antenna elements):

$\begin{matrix}{{\hat{c}}_{b} = {\begin{bmatrix}{\hat{c}}_{b\; 1} \\{\hat{c}}_{b\; 2} \\\vdots\end{bmatrix} = {{\begin{bmatrix}w_{1} & w_{2} & {\ldots\mspace{11mu}}\end{bmatrix}^{H}c_{el}} = {W^{H}c_{el}}}}} & (1) \\{{\hat{c}}_{el} = {\left( {WW}^{H} \right)^{- 1}W\;{\hat{c}}_{b}}} & (2)\end{matrix}$

In these equations, X^(H) denotes the Hermitian transpose of matrix X,the parameter ĉ_(bk) represents the estimated channel coefficients inthe beam space after applying a precoder weight w_(k) and is found asĉ_(bk)=w_(k) ^(H)c_(el), where c_(el) is the channel coefficient vector(of dimension N-by-1) in the channel element space, and the parameterĉ_(el) represents the estimated channel coefficients in the antennaelement space. The matrix pseudo-inverse (WW^(H))⁻¹W is used in Equation(2) to cover the case where M>N. Hence, according to an embodiment therelation used in step S106 is defined by a pseudo-inverse of theprecoder weights.

For the case M=N orthogonal beams, as given by orthogonal precoderweights, (for example DFT beams) can (or in some aspects even needs) beused. Hence, according to an embodiment where M=N, the M beams 110 a,110 b, 110M are mutually orthogonal with respect to each other.

The channel estimator in Equation (2) is a zero forcing estimator whichhas good performance at high SNR. Hence, according to an embodiment therelation used in step S106 is defined by a zero-forcing estimator of thechannel conditions for the N antenna elements 160 a, 160N.

At low SNR, a linear minimum mean square error (LMMSE) estimator couldbe more suitable. Hence, according to an embodiment the relation used instep S106 is defined by an LMMSE estimator of the channel conditions forthe N antenna elements 160 a, 160N. For LMMSE the estimated channelcoefficients in the antenna element space are given as:ĉ _(el)=(R _(el) ⁻¹ +WR _(nb,nb) ⁻¹ W ^(H))⁻¹ WR _(nb,nb) ⁻¹ ĉ _(b)  (3)

In this equation, R_(el)=E[c_(el)c_(el) ^(H)], where E[x] is themathematical expectation of x, the parameter R_(nb,nb) is a matrixrepresenting correlation of the noise in the beam space, and X⁻¹ denotesthe inverse of matrix X. The parameter R_(el) is not invertible unlessthe channel has full rank. By using the matrix inversion lemma theestimated channel coefficients in the antenna element space for LMMSEcan therefore be formulated as:ĉ _(el)=[R _(el) −R _(el)(R _(el)+(WR _(nb,nb) ⁻¹ W ^(H))⁻¹)⁻¹ R_(el)]WR _(nb,nb) ⁻¹ ĉ _(b)  (4)

The beam and channel estimation in the radio transceiver device 200 isperformed per antenna port at the access node 300 a, meaning that theherein disclosed embodiments could be applied in the case with multipleports at the access node 300 a, for example where each port mayrepresent a beam or antenna.

It could be possible to estimate the channel coefficients in the antennaelement space for M<N, for example if side information regarding designof aperture and model for correlation between antenna elements isprovided and consider by the radio transceiver device 200. Hence in someembodiments M<N, and the relation in step S106 utilizes correlationsbetween the N antenna elements 160 a, 160N.

There could be different ways for the wireless device 200 to obtain thechannel conditions for the M beams 110 a, 110 b, 110M in step S104.

In some aspects the channel conditions for the M beams 110 a, 110 b,110M are instantaneous channel conditions. Hence, according to anembodiment the wireless device 200 is configured to perform steps S104a, S104 b as part of step S104:

S104 a: The wireless device 200 sweeps through the M beams 110 a, 110 b,110M, and whilst doing so performs step S104 b:

S104 b: The wireless device 200 receives the signals in the M beams 110a, 110 b, 110M.

If the channel conditions for the M beams 110 a, 110 b, 110M areinstantaneous channel conditions then it could be conditioned that thechannel conditions are not only stationary but static. The channelconditions for the N antenna elements 160 a, 160N could then be(instantaneous) channel estimates of the radio propagation channel.

The above procedure involving Equations (1) and (2) assumes that thechannel coefficients c_(el) are stable during the measurements. If,however, the radio propagation channel between the access node 300 a andthe radio transceiver device 200 is changing quicker than preferred, amore robust procedure could be used. Hence, in some aspects the channelconditions for the M beams 110 a, 110 b, 110M are not instantaneouschannel conditions. According to an embodiment the channel conditionsfor the M beams 110 a, 110 b, 110M are then representative of channelestimations for the M beams 110 a, 110 b, 110M as averaged over multipletime and/or frequency samples.

In this more robust procedure, instead of using instantaneous channelestimates to find (and apply) appropriate settings for the phaseshifters, an averaging of channel estimations over multiple time samplecan be used to attain a covariance matrix in the beam space (denotedR_(b)). Then the covariance matrix in the element space (denoted R_(el))can be determined by solving for the parameter R_(el) in the equation:R _(b) =W R _(el) W ^(H)  (5)

Then, R_(el) is used to find appropriate phase shifter settings at theradio transceiver device 200, which phase shifter settings are morerobust for time varying channel conditions. More strictly, the relationbetween the covariance matrices in the antenna element space and thebeams space is given by:R _(el)=(WW ^(H))⁻¹ WR _(b) W ^(H)(WW ^(H))⁻¹  (6)

In an embodiment also channel estimations from interfering transmitters,such as an interfering access nodes 300 b are determined and taken intoaccount when finding the optimal phase shifter settings. Hence,according to an embodiment the wireless radio transceiver device 200 isserved by an access node 300 a, and the channel conditions for the Mbeams 110 a, 110 b, 110M are indicative of the signals as received fromthe access node 300 a as well as interfering signals received from atleast one other access node 300 b. In such embodiments it is possible tooptimize for example the received signal to interference plus noiseratio (SINR) or estimated throughput.

The estimated channel conditions could by the wireless radio transceiverdevice 200 be used to calculate optimal phase settings of phaseshifters. Hence, according to an embodiment each of the N antennaelements 160 a, 160N has its own phase shifter (as in FIG. 2), and thebeamforming weights determine settings for the phase shifters. Thewireless radio transceiver device 200 could then be configured toperform step S108 a:

S108 a: The wireless radio transceiver device 200 determines updatedsettings for the phase shifters based on the channel conditions for theN antenna elements 160 a, 160N.

Additionally, or alternatively, the estimated channel conditions couldby the wireless radio transceiver device 200 be used to calculateoptimal settings of amplitude tapers. Hence, according to an embodimenteach of the N antenna elements 160 a, 160N has its own amplitude taper,and the beamforming weights determine settings for the amplitude tapers.The wireless radio transceiver device 200 could then be configured toperform step S108 b:

S108 b: The wireless radio transceiver device 200 determines updatedsettings for the amplitude tapers based on the channel conditions forthe N antenna elements 160 a, 160N.

According to some aspects the channel conditions for the N antennaelements 160 a, 160N are indicative of at least one of SINR of thereceived signals and channel throughput of the radio propagationchannel. The updated settings for the phase shifters and/or theamplitude tapers could then be determined to optimize the SINR and/orthe channel throughput.

FIG. 5 is a flowchart of a particular embodiment for obtaining channelconditions per antenna element of the wireless radio transceiver device200 as performed by the radio transceiver device 200 based on at leastsome of the above disclosed embodiments.

S201: The radio transceiver device 200 evaluates if the radiopropagation channel is stationary enough. If the radio propagation isdetermined to be stationary, step S202 is entered, and else step S205 isentered. One way to implement step S201 is to perform step S102.

S202: The radio transceiver device 200 selects M orthogonal beams 110 a,119 b, . . . , 110M. The radio transceiver device 200 then sweepsthrough these M beams 110 a, 119 b, . . . , 110M one at a time, and forevery beam 110 a, 119 b, . . . , 110M the radio transceiver device 200estimates the channel in the beam space. One way to implement step S202is to perform any of step S104 and S104 a.

S203: The radio transceiver device 200, when the channel estimate forall the M beams 110 a, 119 b, . . . , 110M have been attained,determines the channel estimate for each of the N antenna element 160 a,160N in the antenna array by using Equation (1) and Equation (2), orEquation (3) and Equation (4), or Equation (5) and Equation (6). One wayto implement step S203 is to perform step S106.

S204: The radio transceiver device 200, when the channel estimates forthe N antenna elements 160 a, 160N are found, determines an optimalphase setting for each phase shifter and/or optimal settings for eachamplitude taper of the analog antenna array in order to optimize somemetric, for example received power. One way to implement step S204 is toperform any of step S108 a and step S108 b.

S205: The radio transceiver device 200 enters a wait state before onceagain entering step S201. In this way the method can be repeatedregularly in order to adapt the phase shifter settings to potentialchanges for the radio propagation channel and/or the transmit beams atthe access node 300 a. Alternatively, the method can be repeated iftriggered by external information, such as information from apositioning system or a gyro that would indicate that the radiotransceiver device 200 has been moved.

In summary, the radio transceiver device 200 in some aspects evaluatesif the communication channel is sufficiently stationary, or even static.If so, the radio transceiver device 200 performs downlink measurementson a number of appropriately chosen beams created by an analogbeamformer. The radio transceiver device 200 then uses the measurementsto calculate a channel estimate on each individual antenna element ofthe analog antenna array. The radio transceiver device 200 could thenuse these channel estimates to calculate optimal phase settings of thephase shifters of the analog array with respect to some metric.

FIG. 6 schematically illustrates, in terms of a number of functionalunits, the components of a radio transceiver device 200 according to anembodiment. Processing circuitry 210 is provided using any combinationof one or more of a suitable central processing unit (CPU),multiprocessor, microcontroller, digital signal processor (DSP), etc.,capable of executing software instructions stored in a computer programproduct 1010 (as in FIG. 10), e.g. in the form of a storage medium 230.The processing circuitry 210 may further be provided as at least oneapplication specific integrated circuit (ASIC), or field programmablegate array (FPGA).

Particularly, the processing circuitry 210 is configured to cause theradio transceiver device 200 to perform a set of operations, or steps,S102-S108 b, S201, S205, as disclosed above. For example, the storagemedium 230 may store the set of operations, and the processing circuitry210 may be configured to retrieve the set of operations from the storagemedium 230 to cause the radio transceiver device 200 to perform the setof operations. The set of operations may be provided as a set ofexecutable instructions.

Thus the processing circuitry 210 is thereby arranged to execute methodsas herein disclosed. The storage medium 230 may also comprise persistentstorage, which, for example, can be any single one or combination ofmagnetic memory, optical memory, solid state memory or even remotelymounted memory. The radio transceiver device 200 may further comprise acommunications interface 220 at least configured for communications withan access node 300 a, 300 b. As such the communications interface 220may comprise one or more transmitters and receivers, comprising analogueand digital components. The processing circuitry 210 controls thegeneral operation of the radio transceiver device 200 e.g. by sendingdata and control signals to the communications interface 220 and thestorage medium 230, by receiving data and reports from thecommunications interface 220, and by retrieving data and instructionsfrom the storage medium 230. Other components, as well as the relatedfunctionality, of the radio transceiver device 200 are omitted in ordernot to obscure the concepts presented herein.

FIG. 7 schematically illustrates, in terms of a number of functionalmodules, the components of a radio transceiver device 200 according toan embodiment. The radio transceiver device 200 of FIG. 7 comprises anumber of functional modules; an obtain module 210 b configured toperform step S104, and a transform module 210 e configured to performstep S106. The radio transceiver device 200 of FIG. 7 may furthercomprise a number of optional functional modules, such as any of adetermine module 210 a configured to perform step S102, a sweep module210 c configured to perform step S104 a, a receive module 210 dconfigured to perform step S104 b, a determine module 210 f configuredto perform step S108 a, and a determine module 210 g configured toperform step S108 b. In general terms, each functional module 210 a-210g may in one embodiment be implemented only in hardware and in anotherembodiment with the help of software, i.e., the latter embodiment havingcomputer program instructions stored on the storage medium 230 whichwhen run on the processing circuitry makes the radio transceiver device200 perform the corresponding steps mentioned above in conjunction withFIG. 7. It should also be mentioned that even though the modulescorrespond to parts of a computer program, they do not need to beseparate modules therein, but the way in which they are implemented insoftware is dependent on the programming language used. Preferably, oneor more or all functional modules 210 a-210 g may be implemented by theprocessing circuitry 210, possibly in cooperation with thecommunications interface 220 and/or the storage medium 230. Theprocessing circuitry 210 may thus be configured to from the storagemedium 230 fetch instructions as provided by a functional module 210a-210 g and to execute these instructions, thereby performing any stepsas disclosed herein.

The radio transceiver device 200 may be provided as a standalone deviceor as a part of at least one further device. For example, the radiotransceiver device 200 may be implemented in, part of, or co-locatedwith, an access node 800 (as in FIG. 8) or a wireless device 900 (as inFIG. 9). Hence, according to some aspects there is provided an accessnode 800 and/or wireless device 900 comprising a radio transceiverdevice 200 as herein disclosed.

Further, a first portion of the instructions performed by the radiotransceiver device 200 may be executed in a first device, and a secondportion of the of the instructions performed by the radio transceiverdevice 200 may be executed in a second device; the herein disclosedembodiments are not limited to any particular number of devices on whichthe instructions performed by the radio transceiver device 200 may beexecuted. Hence, the methods according to the herein disclosedembodiments are suitable to be performed by a radio transceiver device200 residing in a cloud computational environment. Therefore, although asingle processing circuitry 210 is illustrated in FIG. 6 the processingcircuitry 210 may be distributed among a plurality of devices, or nodes.The same applies to the functional modules 210 a-210 g of FIG. 7 and thecomputer program 1020 of FIG. 10 (see below).

FIG. 10 shows one example of a computer program product 1010 comprisingcomputer readable storage medium 1030. On this computer readable storagemedium 1030, a computer program 1020 can be stored, which computerprogram 1020 can cause the processing circuitry 210 and theretooperatively coupled entities and devices, such as the communicationsinterface 220 and the storage medium 230, to execute methods accordingto embodiments described herein. The computer program 1020 and/orcomputer program product 1010 may thus provide means for performing anysteps as herein disclosed.

In the example of FIG. 10, the computer program product 1010 isillustrated as an optical disc, such as a CD (compact disc) or a DVD(digital versatile disc) or a Blu-Ray disc. The computer program product1010 could also be embodied as a memory, such as a random access memory(RAM), a read-only memory (ROM), an erasable programmable read-onlymemory (EPROM), or an electrically erasable programmable read-onlymemory (EEPROM) and more particularly as a non-volatile storage mediumof a device in an external memory such as a USB (Universal Serial Bus)memory or a Flash memory, such as a compact Flash memory. Thus, whilethe computer program 1020 is here schematically shown as a track on thedepicted optical disk, the computer program 1020 can be stored in anyway which is suitable for the computer program product 1010.

The inventive concept has mainly been described above with reference toa few embodiments. However, as is readily appreciated by a personskilled in the art, other embodiments than the ones disclosed above areequally possible within the scope of the inventive concept, as definedby the appended patent claims.

The invention claimed is:
 1. A method for obtaining channel conditionsper antenna element, the method being performed by a wireless radiotransceiver device comprising N antenna elements in an antenna arraywith analog beamforming and being configured to communicate utilizingbeams, the method comprising: determining that a radio propagationchannel between the wireless radio transceiver device and another radiotransceiver device is stationary; in response to determining that theradio propagation channel between the wireless radio transceiver deviceand the another radio transceiver device is stationary, obtaining, forthe stationary radio propagation channel between the wireless radiotransceiver device and the another radio transceiver device, channelconditions for signals received by the wireless radio transceiver devicein M beams, where M>1; and transforming the channel conditions for the Mbeams to channel conditions for the N antenna elements by utilizing arelation based on beamforming weights that map the N antenna elements tothe M beams.
 2. The method of claim 1, wherein the radio propagationchannel is free from fast fading when the channel conditions for the Mbeams are obtained.
 3. The method of claim 1, wherein M>N.
 4. The methodof claim 1, wherein M=N, and wherein the M beams are mutually orthogonalwith respect to each other.
 5. The method of claim 1, wherein M<N, andwherein the relation specifies correlations between the N antennaelements.
 6. The method of claim 1, wherein the beamforming weights areprecoder weights.
 7. The method of claim 6, wherein the relation isdefined by a pseudo-inverse of the precoder weights.
 8. The method ofclaim 1, wherein the relation is defined by a zero-forcing estimator ofthe channel conditions for the N antenna elements.
 9. The method ofclaim 1, wherein the relation is defined by a linear minimum mean squareerror estimator of the channel conditions for the N antenna elements.10. The method of claim 1, wherein each of the N antenna elements hasits own phase shifter, and wherein the beamforming weights determinesettings for the phase shifters, the method further comprising:determining updated settings for the phase shifters based on the channelconditions for the N antenna elements.
 11. The method of claim 1,wherein each of the N antenna elements has its own amplitude taper, andwherein the beamforming weights determine settings for the amplitudetapers, the method further comprising: determining updated settings forthe amplitude tapers based on the channel conditions for the N antennaelements.
 12. The method of claim 1, wherein the channel conditions forthe N antenna elements are indicative of at least one of signal tointerference plus noise ratio, SINR, of the received signals, andchannel throughput of the radio propagation channel.
 13. The method ofclaim 1, wherein the wireless radio transceiver device is served by theanother radio transceiver device, and wherein the channel conditions forM beams are indicative of the signals as received from the another radiotransceiver device as well as interfering signals received from at leastone other radio transceiver device.
 14. The method of claim 1, whereinobtaining the channel conditions for the M beams further comprises:sweeping through the M beams, and whilst doing so: receiving the signalsin the M beams.
 15. The method of claim 1, wherein the channelconditions for the M beams are representative of channel estimations forthe M beams as averaged over multiple time and/or frequency samples. 16.The method of claim 1, wherein the channel conditions for the N antennaelements are channel estimates of the radio propagation channel.
 17. Themethod of claim 1, wherein transforming the channel conditions for the Mbeams to channel conditions for the N antenna elements comprisescalculating W^(H)C_(el), where W^(H) is a Hermitian transpose of amatrix W and C_(el) is a channel coefficient vector.
 18. The method ofclaim 1, wherein transforming the channel conditions for the M beams tochannel conditions for the N antenna elements comprises calculating:(WW^(H))⁻¹W W^(H) C_(el), where W is a matrix, W^(H) is a Hermitiantranspose of the matrix W, and C_(el) is a channel coefficient vector.19. The method of claim 1, wherein transforming the channel conditionsfor the M beams to channel conditions for the N antenna elementscomprises calculating equation (3), equation (4) or equation (6) asdescribed in the specification.
 20. The method of claim 1, whereindetermining that the radio propagation channel between the wirelessradio transceiver device and the another radio transceiver device isstationary comprises: determining a value indicating a change in theradio propagation channel, comparing the value to a threshold, anddetermining that the value is less than the threshold.
 21. A first radiotransceiver device for obtaining channel conditions per antenna element,the first radio transceiver device comprising N antenna elements in anantenna array with analog beamforming and being configured tocommunicate utilizing beams, the first radio transceiver device furthercomprising: processing circuitry; and a non-transitory storage mediumstoring instructions that, when executed by the processing circuitry,cause the first radio transceiver device to: determine that a radiopropagation channel between the first radio transceiver device and asecond radio transceiver device is stationary; in response todetermining that the radio propagation channel between the first radiotransceiver device and the second radio transceiver device isstationary, obtain, for the stationary radio propagation channel betweenthe first radio transceiver device and the second radio transceiverdevice, channel conditions for signals received by the first or secondradio transceiver device in M beams, where M>1; and transform thechannel conditions for the M beams to channel conditions for the Nantenna elements by utilizing a relation based on beamforming weightsthat map the N antenna elements to the M beams.
 22. The first radiotransceiver device of claim 21, wherein the first radio transceiverdevice is one of: an access node or a user equipment (UE).
 23. Acomputer program product comprising a non-transitory computer readablemedium storing a computer program for obtaining channel conditions perantenna element, the computer program comprising computer code which,when run on processing circuitry of a first radio transceiver devicecomprising N antenna elements in an antenna array with analogbeamforming and being configured to communicate utilizing beams, causesthe first radio transceiver device to: determine that a radiopropagation channel between the first radio transceiver device and asecond radio transceiver device is stationary; in response todetermining that the radio propagation channel between the first radiotransceiver device and the second radio transceiver device isstationary, obtain, for the stationary radio propagation channel betweenthe first radio transceiver device and the second radio transceiverdevice, channel conditions for signals received by the first or secondradio transceiver device in M beams, where M>1; and transform thechannel conditions for the M beams to channel conditions for the Nantenna elements by utilizing a relation based on beamforming weightsthat map the N antenna elements to the M beams.